null_blk: Fix locking in zoned mode

When the zoned mode is enabled in null_blk, Serializing read, write
and zone management operations for each zone is necessary to protect
device level information for managing zone resources (zone open and
closed counters) as well as each zone condition and write pointer
position. Commit 35bc10b2eafb ("null_blk: synchronization fix for
zoned device") introduced a spinlock to implement this serialization.
However, when memory backing is also enabled, GFP_NOIO memory
allocations are executed under the spinlock, resulting in might_sleep()
warnings. Furthermore, the zone_lock spinlock is locked/unlocked using
spin_lock_irq/spin_unlock_irq, similarly to the memory backing code with
the nullb->lock spinlock. This nested use of irq locks wrecks the irq
enabled/disabled state.

Fix all this by introducing a bitmap for per-zone lock, with locking
implemented using wait_on_bit_lock_io() and clear_and_wake_up_bit().
This locking mechanism allows keeping a zone locked while executing
null_process_cmd(), serializing all operations to the zone while
allowing to sleep during memory backing allocation with GFP_NOIO.
Device level zone resource management information is protected using
a spinlock which is not held while executing null_process_cmd();

Fixes: 35bc10b2eafb ("null_blk: synchronization fix for zoned device")
Signed-off-by: Damien Le Moal <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/null_blk.h

···
 	unsigned int nr_zones_closed;
 	struct blk_zone *zones;
 	sector_t zone_size_sects;
-	spinlock_t zone_lock;
+	spinlock_t zone_dev_lock;
+	unsigned long *zone_locks;
 
 	unsigned long size; /* device size in MB */
 	unsigned long completion_nsec; /* time in ns to complete a request */

drivers/block/null_blk_zoned.c

···
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/vmalloc.h>
+#include <linux/bitmap.h>
 #include "null_blk.h"
 
 #define CREATE_TRACE_POINTS
···
 	if (!dev->zones)
 		return -ENOMEM;
 
-	spin_lock_init(&dev->zone_lock);
+	spin_lock_init(&dev->zone_dev_lock);
+	dev->zone_locks = bitmap_zalloc(dev->nr_zones, GFP_KERNEL);
+	if (!dev->zone_locks) {
+		kvfree(dev->zones);
+		return -ENOMEM;
+	}
+
 	if (dev->zone_nr_conv >= dev->nr_zones) {
 		dev->zone_nr_conv = dev->nr_zones - 1;
 		pr_info("changed the number of conventional zones to %u",
···
 
 void null_free_zoned_dev(struct nullb_device *dev)
 {
+	bitmap_free(dev->zone_locks);
 	kvfree(dev->zones);
+}
+
+static inline void null_lock_zone(struct nullb_device *dev, unsigned int zno)
+{
+	wait_on_bit_lock_io(dev->zone_locks, zno, TASK_UNINTERRUPTIBLE);
+}
+
+static inline void null_unlock_zone(struct nullb_device *dev, unsigned int zno)
+{
+	clear_and_wake_up_bit(zno, dev->zone_locks);
 }
 
 int null_report_zones(struct gendisk *disk, sector_t sector,
···
 {
 	struct nullb *nullb = disk->private_data;
 	struct nullb_device *dev = nullb->dev;
-	unsigned int first_zone, i;
+	unsigned int first_zone, i, zno;
 	struct blk_zone zone;
 	int error;
 
···
 	nr_zones = min(nr_zones, dev->nr_zones - first_zone);
 	trace_nullb_report_zones(nullb, nr_zones);
 
-	for (i = 0; i < nr_zones; i++) {
+	zno = first_zone;
+	for (i = 0; i < nr_zones; i++, zno++) {
 		/*
 		 * Stacked DM target drivers will remap the zone information by
 		 * modifying the zone information passed to the report callback.
 		 * So use a local copy to avoid corruption of the device zone
 		 * array.
 		 */
-		spin_lock_irq(&dev->zone_lock);
-		memcpy(&zone, &dev->zones[first_zone + i],
-		       sizeof(struct blk_zone));
-		spin_unlock_irq(&dev->zone_lock);
+		null_lock_zone(dev, zno);
+		memcpy(&zone, &dev->zones[zno], sizeof(struct blk_zone));
+		null_unlock_zone(dev, zno);
 
 		error = cb(&zone, i, data);
 		if (error)
···
 	return nr_zones;
 }
 
+/*
+ * This is called in the case of memory backing from null_process_cmd()
+ * with the target zone already locked.
+ */
 size_t null_zone_valid_read_len(struct nullb *nullb,
 				sector_t sector, unsigned int len)
 {
···
 	if (zone->type == BLK_ZONE_TYPE_CONVENTIONAL)
 		return null_process_cmd(cmd, REQ_OP_WRITE, sector, nr_sectors);
 
+	null_lock_zone(dev, zno);
+	spin_lock(&dev->zone_dev_lock);
+
 	switch (zone->cond) {
 	case BLK_ZONE_COND_FULL:
 		/* Cannot write to a full zone */
-		return BLK_STS_IOERR;
+		ret = BLK_STS_IOERR;
+		goto unlock;
 	case BLK_ZONE_COND_EMPTY:
 	case BLK_ZONE_COND_CLOSED:
 		ret = null_check_zone_resources(dev, zone);
 		if (ret != BLK_STS_OK)
-			return ret;
+			goto unlock;
 		break;
 	case BLK_ZONE_COND_IMP_OPEN:
 	case BLK_ZONE_COND_EXP_OPEN:
 		break;
 	default:
 		/* Invalid zone condition */
-		return BLK_STS_IOERR;
+		ret = BLK_STS_IOERR;
+		goto unlock;
 	}
 
 	/*
···
 		else
 			cmd->rq->__sector = sector;
 	} else if (sector != zone->wp) {
-		return BLK_STS_IOERR;
+		ret = BLK_STS_IOERR;
+		goto unlock;
 	}
 
-	if (zone->wp + nr_sectors > zone->start + zone->capacity)
-		return BLK_STS_IOERR;
+	if (zone->wp + nr_sectors > zone->start + zone->capacity) {
+		ret = BLK_STS_IOERR;
+		goto unlock;
+	}
 
 	if (zone->cond == BLK_ZONE_COND_CLOSED) {
 		dev->nr_zones_closed--;
···
 	if (zone->cond != BLK_ZONE_COND_EXP_OPEN)
 		zone->cond = BLK_ZONE_COND_IMP_OPEN;
 
+	spin_unlock(&dev->zone_dev_lock);
 	ret = null_process_cmd(cmd, REQ_OP_WRITE, sector, nr_sectors);
+	spin_lock(&dev->zone_dev_lock);
 	if (ret != BLK_STS_OK)
-		return ret;
+		goto unlock;
 
 	zone->wp += nr_sectors;
 	if (zone->wp == zone->start + zone->capacity) {
···
 			dev->nr_zones_imp_open--;
 		zone->cond = BLK_ZONE_COND_FULL;
 	}
-	return BLK_STS_OK;
+	ret = BLK_STS_OK;
+
+unlock:
+	spin_unlock(&dev->zone_dev_lock);
+	null_unlock_zone(dev, zno);
+
+	return ret;
 }
 
 static blk_status_t null_open_zone(struct nullb_device *dev, struct blk_zone *zone)
···
 				   sector_t sector)
 {
 	struct nullb_device *dev = cmd->nq->dev;
-	unsigned int zone_no = null_zone_no(dev, sector);
-	struct blk_zone *zone = &dev->zones[zone_no];
-	blk_status_t ret = BLK_STS_OK;
+	unsigned int zone_no;
+	struct blk_zone *zone;
+	blk_status_t ret;
 	size_t i;
 
-	switch (op) {
-	case REQ_OP_ZONE_RESET_ALL:
+	if (op == REQ_OP_ZONE_RESET_ALL) {
 		for (i = dev->zone_nr_conv; i < dev->nr_zones; i++) {
+			null_lock_zone(dev, i);
 			zone = &dev->zones[i];
 			if (zone->cond != BLK_ZONE_COND_EMPTY) {
+				spin_lock(&dev->zone_dev_lock);
 				null_reset_zone(dev, zone);
+				spin_unlock(&dev->zone_dev_lock);
 				trace_nullb_zone_op(cmd, i, zone->cond);
 			}
+			null_unlock_zone(dev, i);
 		}
 		return BLK_STS_OK;
+	}
+
+	zone_no = null_zone_no(dev, sector);
+	zone = &dev->zones[zone_no];
+
+	null_lock_zone(dev, zone_no);
+	spin_lock(&dev->zone_dev_lock);
+
+	switch (op) {
 	case REQ_OP_ZONE_RESET:
 		ret = null_reset_zone(dev, zone);
 		break;
···
 		ret = null_finish_zone(dev, zone);
 		break;
 	default:
-		return BLK_STS_NOTSUPP;
+		ret = BLK_STS_NOTSUPP;
+		break;
 	}
+
+	spin_unlock(&dev->zone_dev_lock);
 
 	if (ret == BLK_STS_OK)
 		trace_nullb_zone_op(cmd, zone_no, zone->cond);
+
+	null_unlock_zone(dev, zone_no);
 
 	return ret;
 }
···
 blk_status_t null_process_zoned_cmd(struct nullb_cmd *cmd, enum req_opf op,
 				    sector_t sector, sector_t nr_sectors)
 {
-	blk_status_t sts;
 	struct nullb_device *dev = cmd->nq->dev;
+	unsigned int zno = null_zone_no(dev, sector);
+	blk_status_t sts;
 
-	spin_lock_irq(&dev->zone_lock);
 	switch (op) {
 	case REQ_OP_WRITE:
 		sts = null_zone_write(cmd, sector, nr_sectors, false);
···
 		sts = null_zone_mgmt(cmd, op, sector);
 		break;
 	default:
+		null_lock_zone(dev, zno);
 		sts = null_process_cmd(cmd, op, sector, nr_sectors);
+		null_unlock_zone(dev, zno);
 	}
-	spin_unlock_irq(&dev->zone_lock);
 
 	return sts;
 }